perf bpf: Add bpf_map() helper

perf bpf: Add bpf_map() helper

To make the declaration of maps more compact, the following patches will
make use of it.

Standardizing on it will allow to add the BTF details, i.e.
BPF_ANNOTATE_KV_PAIR() (tools/testing/selftests/bpf/bpf_helpers.h)
transparently.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Yonghong Song <yhs@fb.com>
Link: https://lkml.kernel.org/n/tip-h3q9rxxkbzetgnbro5rclqft@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>